Patent GB-1352051-A (GB)
Title: Structural materials
IPC: B29C48/00
Filed: 1971-04-22
Abstract: 1352051 Extruded foamed sheet MITSUBISHI RAYON CO Ltd and SHIN-KOBE ELECTRIC MACHINERY CO Lt 2  22 April 1971 [24 April 1970] 10837/71 Heading B5A [Also in Division C3] A multi-layer extruded synthetic resin board of a configuration which is planar, or as shown in Fig. 2, comprises one or more foamed resin layers 3 intermediate and fused during extrusion to unfoamed resin layers 1, 2. The layers are extruded from a die passage 19 to which they are delivered by die passages 16, and 17, 18, via "coat hanger" type manifolds, Fig. 6, the temperature of the resins decreasing along the passage 19 and the layer 3 issuing unfoamed from the outlet 20 of die lips 21, 22 and expanding to a density of 0À8 to 0À2 gm/cm<SP>3</SP>, effected by a volume increase of 1À3 to 5 times and determined by rolls 14, 15 which are followed by guide rolls, take-up rolls, and a cutter. The rolls 14, 15 are surface coated with hard chromium plating and are of a double shell construction defining a cavity within which hot water or oil is circulated and the peripheral surface speed difference between the rolls 14, 15 and the takeup rolls is adjustable. The die lips 20-21 are transversely adjustable, Fig. 4 (not shown), by bolts (23), and a transversely adjustable choke bar is provided in each of the passages, 16-18, which are each supplied by a variable speed screw extruder. To prevent the formation of excessively large cells (2), Fig. 8 (not shown), at the inter layer boundary, the temperature of the unfoamed layers within the passage 19 is maintained less than 10 C. above that of the foamable layer. Temperature control of the die is maintained by independent electric heating panels, Fig. 3 (not shown), the heaters nearer the die edges being maintained at temperatures 2-5 C. above that of the intermediate heaters to maintain an even temperature across the width of the die. The resins may comprise A-B-S co-polymer, polystyrene, polyethylene, or polyvinyl chloride and the layers may comprise different resins, or the same resin having each layer differently coloured. In the Examples, boards are extruded comprising: (1 and 2), 4 mm thick azodicarbamide foamed A-B-S resin intermediate 1 mm. unfoamed A-B-S layers, each layer being of the same or of a different colour, and the board being of 0À7 gm/cc., (3) similar thickness layers in a board of 0À8 gm./c.c., the foamed layer comprising A-B-S resin foamed by 0À2% azodicarbonamide between layers respectively comprising A-B-S resin, and a copolymer of styrene, methylmethacrylate, acrylonitrile, and acrylic rubber; (4), similar thickness layers and density of board, the foamed resin and one exterior layer being of the same resins as in Example (3), and the other layer being a copolymer of acrylic rubber, acrylonitrile and styrene. Test results are given relating to the rigidity and the shock absorption properties of the Example (2) board, a similar board having 2 mm. thick surface layers, and boards of the same weight comprising aluminium sheet, glass fibre reinforced polyester sheet, steel sheet, and A-B-S sheet; and also relating to exposure resistance, as measured by impact strength, of the Examples (2) and (3) materials in comparison with single layer 1 mm. sheets of the co-polymer resins of these examples. The boards of different coloured exterior layers may be utilized in boat building. A desired weathering or combustion resistance may be effected in one exterior layer by incorporating suitable resisting agents. The board may be used in signboards or improved resistance to ultra-violet rays when one surface layer comprises an acrylic rubber co-polymer, comprising butyl acrylate; acrylonitrile and styrene; a copolymer comprising butyl acrylate, acrylonitrile, styrene and methyl methacrylate; or copolymers comprising butyl acrylate, acrylonitrile, styrene, methyl methacrylate and n-butyl acrylate. The blowing agents may also comprise 0À1-2À0% dinitrosopentanemethyltetramine, or 1-8% methane or butane as a resin impregnant.